Inhibiting polymer precipitation in acetylene purification process



INHIBITING POLYMER PRECIPITATION 1N ACET- PURIFICATION PROCESS Robert Bird Johnson and Leslie Hunt Sutherland, New

Orleans, La., assignors to American Cyanamid Company, New York, N.Y., a corporation of Maine No Drawing. Application October 26, 1956 Serial No. 618,443

7 Claims. (Cl. 260679) This invention rel-ates to the purifica'tionof an acetylenebearing gas. More particularly, it relates to inhibiting polymer precipitation in a solvent selective in its action to acetylenes. i

In the manufacture of acetylene from hydrocarbons, e.g., by the partial oxidation of natural gas, the resultant acetylene-bearing gas is generally purified by treating it with a selective solvent whereby substantially all the acetylene as well as the higher acetylenes are absorbed,

' while the less soluble components pass oif in the oil-gas stream. The resultant solution of acetylenes is then treated to separate acetylene from the higher acetylenes and both from the solvent, the solvent then being recycled. Various solvents have been proposed and effectively employed in this purification system, one of the preferred being butyrolactone.

Although this purification system has been commercially employed to a considerable extent, it suifers from one serious disadvantage. Because of the presence of higher acetylenes in the reaction gas and the use of elevated temperatures in the purification system, polymer formation occurs. Polymer thus formed builds up in the solvent and tends to precipitate particularly in the presence of Water. Resultant accumulations of polymer solids in the heat exchangers, stripping columns, lines and the like necessitates periodic shutdowns of equipment thus seriously limiting production.

One suggested method of minimizing the polymer content of the solvent is to treat a continuously withdrawn small slip stream of stripped solvent with water to precipitate polymer which can then be separated by filtration prior to recycling of the solvent. This is not wholly satisfactory because of filtration problems caused by the fine size of the polymer. In addition, the problem of polymer precipitation within the purification system is aggravated because of the possibility of introducing additional water into the solvent. It also has been proposed to combat this problem by adding any of various chemical agents to the solvent believed to be capable of stabilizing the solution of higher acetylenes against polymerization. Although numerous materials have been proposed, none has been found to be particularly effective in reducing polymer formation. 55

There has continued to remain, therefore, a need for inhibiting the problem of polymer formation in the purification of acetylene. Particularly, there has been a con- 2,907,801 Patented Qct 6, 19 59 tinued need for reducing the frequency of shutdowns of the purification system for cleaning necessitated by the accumulation of precipitated polymer.

In accordance with this inventiomthese needs are met to a most unusual and unexpected degree. It now has been found that the precipitation of polymer can be greatly inhibited by incorporating in the solvent a compound of the formula in which R, and R are radicals selected from hydrogen,

alkyls of 1-4 carbon atomsyand phenyl; and R isa radical selected from H, NO, N0 OH, COOH'and CHO.

Illustrative of such compounds are aniline, methylaniline, dimethylaniline, benzylamine, o, m, and p-aminophenol, o, m, and p-nitroaniline, p-nitrosodimethylaniline, o-nitro- N-phenylaniline, p-nitroso-N-phenylaniline, 2-nitroand 4-nitroso-diphenylamine, 4-dimethylaminobenzaldehyde, p-aminobenzoic acid and the like. In contrast to the previous use of chemical addition agents which are alleged to overcome the polymerization problem by stabilizing the solution, the agents of this invention do not reduce polymerization but appear to inhibit the precipitation of solids by forming a polymer considerably more soluble in a. selective solvent or solvent-water system than heretofore obtained. At any rate, regardless of how it functions, the precipitation and accumulation of solids in the acetylene purification system is substantially reduced by the presence in the system of an inhibitor according to this invention.

The amount of inhibitor employed may be quite widely varied. Precipitation of polymer has been. considerably inhibited in a solution containing as little as 0.01% by weight of inhibitor. Generally, the amount of inhibitor will be greater than this and may range to as high as 5% or more, although little added advantage appears to be gained by using these higher amounts. Usually, therefore, the amount of inhibitor will be less ranging from about 0.1% to about 1.0%;

To avoid a build up of soluble polymer in the solvent, a continuous slip stream of stripped solvent may be withdrawn and treated by any means which form no part of this invention to separate the polymer.

The following examples furtherillustrate the invention. Unless otherwise noted, all parts are by weight.

EXAMPLE Samples comprising 50 parts water, 50 parts butyrolactone, 0.25 part diacetylene and each containing an inhibitor acording to Table I are placed in sealed tubes and heated for 16 hours at C. Two additional samples, sample 1 containing no inhibitor, and sample 2 containing no inhibitor and no diacetylene, are used as controls and similarly treated. Each sample is then observed for polymer precipitation.

Table Inhibitor Sample Number m-Aminopheno o-Nitroaniline.

o-Nitro-N-phenylaniline..-

p-Nitroso dimethylanilina p-Nitroso-N-phenylaniline 4-nitrosodiphenylamine- 4-d1methylaminobenzeldehyde- N,N-dimethyla.nilinn Polymer precipitation after 16 hours Slight N o N o Similar results are obtained using other inhibitors in varying amounts in accordance with this invention. Polymer precipitation is also inhibited in the same manner when using selective solvents other than butyrolactone.

1. The method of inhibiting polymer precipitation in the preparation of acetylene in which an acetylene-bearing gas 'is treated with butyrolactone whereby acetylene and higher acetylenes'a're absorbed which comprises carrying out the absorption in the presence of a compound-0f the formula in wh ich R and R are radicals selected from hydrogen, alky ls of 14 carbon atoms, and phenyl; and R is a radical selectedfrom H, NO, N0 OH, COOH, and CH0.

, 4" r v. 2. A process according to claim 1 in which R and R are hydrogen and R is OH.

3. A process according to claim 1 in which R and R are hydrogen and R is N0 4. A process according to claim 1 in which R and R are phenyl and R is N0 5. A process according to claim 1 in which R and R are phenyl and R is NO.

6. A process according to claim 1 in which R and R References Cited in the file of this patent UNITED STATES PATENTS 1914979 cam a 1 Aug-291, 193; 2, 5, 02 el on Aug- 91; 55 2,715,105 Nelson Aug. 9, 19'55'v 

1. THE METHOD OF INHIBITING POLYMER PRECIPITATION IN THE PREPARATION OF ACETYLENE IN WHICH AN ACTEYLENE-BEARING GAS IN TREATED WITH BUTYROLACTONE WHEREBY ACETYLENE AND HIGHER ACETYLENES ARE ABSORBED WHICH COMPRISES CARRYING OUT THE ABSORPTION IN THE PRESENCE OF A COMPOUND OF THE FORMULA 